Vitrified diamond grinding wheel



Aug. 29, 1944. R. H. LOMBARD 2,356,938

VITRIFIED DIAMOND GRINDING WHEEL Filed Jan. e, 1942 F151l Haz 2f @wim-'Wmv 2 'H52 230 WMV/IAM 230 lar la 76 f2A f7 RDBERT H. LOMBARD www Patented 'Aug'. v29, 1944 VITRIFIED DIAMOND GRINDIN G WHEEL Robert H. Lombard, Worcester, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachuset Application January '6, 1942, Serial No. 425,803

4 Claims.` v(Cl. 51-307).

The invention relates vto vitried diamond grinding wheels.

One object of the invention is to. provide a technique for the manufacture of vitrifled bonded diamond. grinding wheels and, sticks or hones which shall be as simple as lpossible and give consistently good results. Another object of the invention is to provide a structure for two-part vitried diamond 'grinding wheels having an abrasive rim or periphery and a non-abrasive center, which structure shall be integral and can be duplicated with few, vif any, rejections during manufacture. n

Another object ofthe invention is to control and prevent swelling of either the center or the abrasive portion of a'. vitrined bonded diamond grinding wheel. Another object of the invention is to provide a mix for a centerfor such a wheel capable of being matured into a 'strong and unlform center in a vitrifying process. Other objects will be in part obvious or in part pointed outhereinafter."

plane abrasive surface because perhapsthe reverse is the fact, but the manufacture of a peripheral ceramic diamond grinding wheel presents particular problems and from the following disclosure the manufacture of a diamond ceramic cup wheel will be vreadily understood. InI the iirst place,it may be noted that owing to the great v cost of diamonds, it isl quite usual to make diamond grinding wheels in the form of a thin The invention accordingly consists in the feaf tures of construction, combinations of elements, arrangements 'of parts, and in the several steps and relation and order of each of said steps to one or more of the others thereof, al1 as will be illustratively described herein, and the scope of y the 'application of which will be indicated in the following claims.

In the accompanying drawing illustrating one of many possible embodiments of the mechanical features of this invention,`

. Figure 1 is a cross sectional view of a mold having just been filled with a vltriiied non-abrasive mix to form the center'of `a peripheral -vitrified diamond grinding wheel; l

Figure 2 shows the mold of Figure 1 with a t'op plate in position; 4 4

Figure 3 shows the mold of Figures 1 and 2 after pressing of the center, after inversion, after the mold ring has been removed and a two-diameter mold band placed outside of the largest mold plate;

Figure 4 shows the mold' inthe same condition of the plate ll I position apair of spacing blocks that of the plate I0. I now remove the blocks, I4

as in Figure 3 after the annular space has been filled with diamond ceramic ,material and the ring reinserted; and

Figure 5 shows themold of Figure 4 after it isclosed. y

` They drawing illustrates the manufacture of a peripheral wheel. Fromthis it -should not be understood-that peripheral wheels are more important or manufactured in greater quantities cun wheels 'and othersv having `,m mmm.

annulus of diamond abrasive with a non-abrasive center. .A ceramic bonded diamond abrasive wheel has certain free-cutting and wear resisting -properties which make it highly desirable for certain grinding operations. It is desirable to make a vitriiled center forv such diamond grinding wheels and in order to make an integral body free from cracks or strains, it is desirable to vitrify the center or back at the same time that the rim is vitrified. j

Swelling is a particular problem and, therefore,

it is important to provide a mix both for the` center and the annulus which will not swell during nring. I shall iirst describe the steps in the molding technique for the productiton of a green body ready for firing in a suitable furnace.

Referring now to Figure 1, I provide a large nat plate t and a mold consisting oi' a -plate I0, a ring Il, and an arbor I2.v 'I'he ring Il just fits the plate i0 and the arbor l2 Just nts in a central hole I3 in the plate Il. I :first place the plate III upon the plate 0 and at oppositie sides I4. I then place the ring II around the plate Ill and upon the blocks I4, as shown. I then insert the arbor I2 part way into thehole Il. I now fill the mold with a center non-abrasive mix Il and level'it off in a well known'man'ner.

I now transfer the illled mold oi' Figure 1 on the plate 9^ to the bottom plate oi!-A a hydraulic press. Referring to Figure2, I now place upon the arbor l2 a plate I I having an arbor hole Il and having a diameter somewhat greater than and temporarily hold up the ring Il` withmy fingers.v Then I 'appiyvthe pressure ofthe `hardraulic press to the extent of about 250 pounds per square inch. f After the'` ring Il 'starts to move, sumcient gritmoves between l:lt andthe plate 'Ill to prevent the ring Il from dropping.:

-I now strip the; mold ring` I'I -andinvert the 'y mold, Alocatingthe plate ,-It on the bcttomfplate of-` the hydraulic*:press., A consolidated center mix laisnow vlocated betweenithe plaies and il.v4 Then I place a heavymold band Ilfaround the plate It' and uponspacinglblocks.lli.;l The -rated therefrom by a shoulder 2I.

mold band I8 has a small inside diameter approximately the same as that of the outside di ameter of the plate I6 so as'to t upon it with a `sliding fit. It has a larger inside diameter sepa- When the band I8 is raised by the blocks I9, the shoulder 2l is somewhere between the top and bottom of the plate I0.

This leaves a space 22 bounded on the bottom by the plate I6, on the outside by the mold band I8, and on the inside by the periphery of the plate I and the periphery of the consolidated center Ia. The top of this space 22 `to be filled is somewhat below the level of the shoulder 2l. Referring to Figure 4, I now ll this space with a. diamond containing ceramic mix 23. I then place the ring II inside the mold band I8 upon the shoulder 2|, as shownl It Will benoted that the height of the ring II is the same as that of the plate Ill but the distance from the shoulder 2| to the top of the mold band I8 is slightly less. I now remove the spacing blocks I9 and close the mold to the position shown in Figure 5. The quantity of material I5 arid 23, respectively, is selected so that the two parts of the wheel will be pressed to definite, predetermined densities or packings of their constituents, and usually so that the two parts of the Wheel will have similar densities of packing, that is, the porosity of the rim and the center will be similar. The closing of the mold tothe position shown in Figure 5, however, further presses the consolidated mix I5a simultaneously with the compression of the lll 23, so that the pressed center I5b and the pressed ll 23a are of equal heightand consolidated into an integral article which can be readily handled even before it is fired. Such an article' is termed a green" wheel in the abrasive industry.

I now strip the mold band I8, remove the plug I2, and then pick off the plate I3 and the plate I0 and ring II. I now have a greenwheel consisting of a non-abrasive center part I5b and an tially, however, the material that is useful in this invention is a reduced compound having most of the oxygen eliminated. Elementary boron and the borides have, at temperatures of l000 C. and also considerably below that temperature, a great afilnity for oxygen. In other Words, boron forms boric oxide B20: (anhydrous) while the borides form borates. Any

boride which is sufficiently stable under ordinary conditions so that it will not decompose with deleterious effects, and which does not volatilize appreciably at 1000*? C., may be used in this invention. I have actually used so-called amorphous boron but crystalline varieties could also be used.

I have also used boron carbide B4G which was first produced by Raymond R. Ridgway but other boron carbides known prior to Ridgway, such as that reported to be BC, may also be used. I have also usedcalcium boride CaBa. Examples of other borides which may be used are: copper boride, CuzBz; barium boride, BaBs; strontium boride, SrBe; beryllium boride; aluminum boride; silicon boride, SIB: or SiBa; zircoabrasive periphery 23a in an integral piece, with v ceramic material throughout capable of being flred in a suitable furnace into an integral nonswelled grinding wheel.

Considering now the materials which I use to form the abrasive periphery 23a and th'e center or backing I5b, 'the yformer contains diamonds while the latter does not; both parts include ceramic materials, and in accordance with the present invention one or both of the parts contains boron, borides, or reduced boron com-- pounds. The use of boron, borides, or oxidizable boron compounds has at least two desirable functions: (l) It prevents detrimental swelling of the abrasive body due to the evolution'of certain gases from the material during the burn in a non-oxidizing atmosphere; and 2) it provides at the same time suitable solid granular material for the vitried bonded framework of the center or backing I5b and desirably also of the periphery 23a. This use of boron, borides, or reduced boron compounds has enabled meto makenon-swelled diamond containing abrasive nium boride, ZraB4; chromium boride, CrB or CrsBz; molybdenum boride, MoaBi; tungsten boride. e

The following examples give, as indicated, usable formulae for the peripheral portion 23a or the center I5b.

EXAMPLE;

Abrasive periphery Diamond abrasive grains, No.v 100 grit SlZe 0.1579

varia '151e'gi'fo aat Borosilicate glass powder between 90 and 140 grit size 0.371 Reduced boron compound, 100 grit size or iiner 162 4% Glutoline solution as a temporary binder and wettant- 0094 TABLE I Frit batch Parts Borax 32.2 Boric acid 25.4 Flint t. 37.6 Hydrate of alumina 1.0 lWhiting 3.8

bodies of excellent quality bonded with a vltried bond matured in the vicinity of 1000 C. or

below in a non-oxidizing atmosphere. i

Boron and the borides can collectively be termed -reduced'boro'n compoun or oxidizable boron compounds. vSucli reduced boronVl compounds may in some cases have a minor amount of oxygen, such as an impurity vconsisting of a small percentage of 4a borate. Eim' The foregoing ingredients of the frit batch are thoroughly mixed, fused, and quenched to form a frit in the usual manner, which is then pulverized.

EXAMPLE II Center or backing Grams assacss 3 III Center or backing Grams vitreous silica, between 100 to 210 .'srit f In the foregmng Example III the vltriilable bond No. 2 is made from 35 parts of Kentucky No. 6 ball clay mixed with 65 partsgt the frit of Table I.-

man rv Center or backing The constituents are thoroughly mixed until a damp. pulverulent, screenable, moldable mix is formed. l

The borosilicate glass referred to has approximately the following composition: 'v

Relatively iugn'fnemng borosmcate glasses are preferred.

'The calculated chemical composition of the frit used is as follows:

size y 0.267 lioroesilicatel glass powder, around 90 grit aise A 0.152' Vitrinable bond No. 2 A 0.320 Reduced boron compound, 180 grit size or Y tlner` 0.595

4% Glutoline solution as va temporary binder and wettant v0,4087

that the use of boron, auch as amorphous boron, or borides such as those herein mentioned, as a whole 'orpart of the granular constituents of the central supporting disk or backing obviates this swellingsatisfactorily, and at the 'same time the reduced lboron compound provides a suitable material for the vitrified bonded framework of Y the supporting center. Here also, as in the diamond containing rim, the reduced` boroncompound serves the dual function of controlling the swelling in a non-oxidizing atmosphere and of serving as a structural element of the center.

It will thus be seen that there has been provided by this invention an article and a method in which the various objects hereinabove set forth together with' many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the mechanicalfeatures of the above invention and `as the art herein described might be varied in various parts, all without departing from the scope of the invention, lt is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing 'issto be interpreted as illug'-,

trative and not in a limiting sense.

I claim: l. A vit nring; of a mix -that 'comprises abrasive grains, granules of an oxidizable boron compound. and

` vitrliiable bond, granules of said compound being present in the vitrified productiin an'amount, exclusive of any oxidation product formed during firing as a result of oxidation of someof said compound, to constitute a substantial proportion Iier cent slof V- a n 80.5 B20: 1 12.9 Also: 2.2

' Haro 3.8 KzO 0.4

of the volume of the vitriiled article and being bonded by, anddistributed in said amount throughout, the vitriiied bond thereby to reinforce the bond and to form with the vitriiied .40 bond a builtdup framework of which the granules 'Ai'wter the' "green" wheels are formed. as' already described. thy are placed in a suitable furnace and burned in a non-oxi ng atmosphere, preferably an `atmosphere or nitrogen, which I have found tobe very effective. Some atmospheres favor the `wetting of the diamonds by the vitriilable bond more than others. Nitro- (en I have found'to be particularly eifectivef or at least nitrogen doesnot inhibit the wetting o( 'the diamonds to any considerable extent.` In or'-l de'r to purify it and eliminate all lpossible traces of said compound, in said substantial proportion, are material structural parts, said abrasive grains being ldistributed throughout, and supported by,

said build-up' framework and bonded'therein by l the vitriiled bond of said framework.

2. A 'vitriiled bonded abrasive article having a unitary body comprising a vitritled-bonded `abrasiveiportlon and a vitried-bondedbacking portion. and being the unitary bonded reactionV l product as a result of nring together two'mixes. one of which comprises abrasive grains and vitrlfiable bond and the other of which comprises vitriilable bond and granules of an oxidiaable' 'boroncompound. granules 'oi' said oxidizable boron compound lbeing present in the vitrinedbonded backing portion in an amount. exclusive of any oxidation product formed during firing as a result of oxidation oi' some of said compound,

' to constitute a substantial proportion structuro! oxygen, the nitrogen should be passed throughy concentrated sulphuric acidand over a red hot copper gauze. The preferred vitrifying conditions constitute 'a temperature of around, 950 C. maintained for four and one-halfyhours.`

A vitrliied bonded supporting centr or back -triade solely ci materials which are nodi-reactive toward the furnace atmosphemv is apt to swell obiectionably when burned even in a non-oxidizing atmosphere due to the evolution of gas from its constituent materials.- This kswelling may seriously disturb the structure oi portions of the peripheral' diamond containing rim which are adlacent to the supporting'center. I have found ally of the said 'backing portion and the said granules being bonded by, and distributed in said substantial proportion through the vitrinea bona or said backing portion to om a buntup framework of which said -oxidizable compound granules are in said amount material structural parts to thereby constitute said lbacking portion to support said abrasive portion.

3. A vitriil'ed bondedV abrasive article having a unitary body comprising a vitriiled-bonded abrasive, portion and a vitrifled-bonded backing portion.' and being the unitary bondedreaction product as a result oi' firing together two mixes, of which comprises abrasive grains and vitriiiable bond and granules of an oxidizableboron compound and the other of which comprises vitrined-bonded abrasive article comprising the bo ded reaction product, as' a result of a able bond and granules of an oxidizable boron compound, granules of said oxidizable boron compound being present in each of said portions in an amount, exclusive of any oxidation product formed during tiring as a result of oxidation of some of said compound, to constitute a substantial proportion structurally of said abrasive portion and of said backing portion and the said granules being in each portion bonded by, and distributed in said substantial proportion throughout, the vitrified bond in each portion to form in each a built-up framework of which said oxidizable compound granules are in said amount material structural parts, said abrasive grains being distributed throughout, and supported by, said builtup framework of the abrasive portion and bonded therein by the vitrified bond in said portion, the built-up framework of the backing portion constituting a support for said abrasive portion.

'4. A vitried-bonded abrasive article having a unitary body comprising a vitrifled-bonded abrasive portion and a vitrified-bonded backing portion, and being the unitary bonded reaction product as a result of firing together two mixes, one of which comprises abrasive grains and vitrinable bond and the other of which comprises vitrifiable bond and granules of an oxidizable boron compound and body material comprising granules of vitreous silica, granules of said oxidizable boron compound and granules of said vitreous silica being present gin the vitrifiedbonded backing portion in an amount, exclusive of any oxidation product formed during tiring as a result of 'oxidation of some of said compound,-

to constitute a substantial proportion structurally of the said backing portion and the said granules of oxidizable compound and the said granules of vitreous silica being bonded by, and distributed in said substantial proportion throughout, the vitrified bond of said backing portion to form a built-up framework of which said oxidizable compound granules and vitreous silica granules are in said amount material structural parts to thereby constitute said backing portion to support said abrasive portion.

ROBERT H. LOMBARD. 

